For a conventional paper making machine, during operation, an operator periodically patrols and monitors it to check the operational state, so as to ensure stable operation of the machine. In order to detect the occurrence of a paper tear, for example, a paper-tear detecting sensor which is constituted by an infrared emitter arranged at the obverse side of running paper and a detector arranged at the reverse side of the running paper is installed in the machine. When the paper tears, the detector detects infrared light, so that the paper tear can be recognized.
With such a paper-tear detecting sensor, while a paper tear can be detected, its cause cannot be determined. For this reason, in recent years, a camera and a light source have been installed around the machine to monitor its state, and also, the monitored state is recorded in a video recorder or a digital memory, so that how the paper breaks can be replayed. In this manner, the operator can determine the cause. This approach, however, merely replays a recorded scene of the situation in which the paper tore, and thus cannot prevent a paper break or tear from occurring. Recently, paper machines have become increasingly faster, and thus it is important to minimize the occurrence of problems, such as paper breaks, in order to improve the production efficiency.
An approach for overcoming the above-described problems is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2000-154489. In this approach, a light source is arranged at one side of the paper surface of paper running on rolls in a paper machine and a plurality of cameras are arranged at the other side, and images of the light transmitted through the running paper from the light source are captured by the plurality of cameras. The amount of variation in release points of the running paper from a roll is quantitatively determined so that the paper machine is monitored for an abnormality.
With the above-described approach, however, release points across the entire width of the running paper are monitored by a plurality of cameras, and thus, when the image-capturing environment is poor due to, for example, the generation of a large amount of mist in the vicinity of a monitoring portion, it is difficult to determine the amount of variations in the positions of release points across the entire width. Further, since the monitoring equipment is installed at both paper surfaces of the running paper, when space for the monitoring portion is limited, it is difficult to install the monitoring equipment in practice. Although this approach is superior in that monitoring is performed using transmitted light that can provide a clearer image, it is inconvenient in practice.